Steel alloy and process of making same



Patented Dec. 12, 1933 PATENT OFFICE STEEL ALLOY AN]; PROCESS OF MAKING John L. Cox, mum... Pa.

No Drawing. Application October 27, 1928 Serial No. 315,593

o 18 Claims. Hy invention relatu to a steel alloy for use at high temperatures which is especially suited for the manufacture of valves for internal combustion engines. Valves of this character in use.

are subject to conditions which tend rapidly to reduce their emciency and shorten their life. The high temperature to which they are subjected has the effect of softening and of scaling the valve heads, so that they deform readily and do not seat properly. Under the influence of heat, the valve stems tend to seize in their bearings. Some steels which are otherwise fairly satisfactory at high temperature are too soft to withstand the blows of the tappets upon the ends of .valve stems made from them, which therefore tend to upset and fail to function properly.

Another cause of failurein such valves is the alteration of'size which occurs in passing from the alpha to the gamma state and vice versa. Most valve steels possess a critical temperature so low that a valve on going into service is heated above its critical range, becomming austenitic in of steel alloyed with nickel, chromium and aluminum, in suitable proportions hereinafter specified, to which are added silicon and manganese in proportions not necessarily substantially diflerent from-those characterizing known .steel alloys.

I have found that aluminum, added to a nickelchromium steel, has for one effect that of raising its critical temperature in the p l rtion, rough- 1y, of 70' F. for each one per cent. of aluminum, which is contrary to the belief held by high authority that aluminum must reduce the critical temperature of steel. Further, aluminum, through its production on oxidation of a thin film of adherent oxide, serves to protect from oxidation the other elements with which it is alloyed.

Nickel in such a combination has for one effect the lowering of the critical temperature of transformation of carbon'steel at a rate of about 145 1". for each per cent. of nickel. In steels with about 10 per cent. of chromium, the effect is much more marked and the transformation temdation.

perature is lowered about 50? I". for each addition of 1% of nickel. Its advantages lie in the increased hardness of the alloy, increased resistance to oxidation, in its production of a tight- 1y adherent scale, and in the fact that in a go chrome-aluminum valve it prevents seizing and galling of the valve stem in its guides.

Furthermore, nickel and aluminum possess the property of combining to form an exceedingly hard alloy having the composition NiALwhich g retains its hardnessat elevated temperatures.

Chromium in high percentages in steel has the effect of increasing the strength of the steel at high temperatures and of strongly resisting oxi- 7o While certain of the-specified characteristics and actions of the metals designated are known, it is believed that other characteristics and actions, especially the effects of associating one metal with another and of adjusting the proportions of the various metals, have not heretofore been known. Certainly their practical application to the solution of the difllcult problem of manufacturing ralvesteel has never occurred to those skilled in the art. With the knowledge, in part known and in part discovered by me, of these absolute and relative qualities, I have found it possible, by a judicious combination of the amounts of nickel, chromium and aluminum, to produce steels that will meet all the exacting requirements for valves. Thus, I havefound it possible, by suitably varying proportions, togive to the steel critical temperatures of transformation higher than the operating temperatures to which different valves are subjected. Further, up to a proportion of aluminum which will render the alloy brittle, say about 7%, the hardness can be increased by increasing the nickel content corresponding but always at the expense of lowering the critical temperature, which may be necessary to permit hardening the ends of the stems.

The proportions of nickel may vary within a wide range, say from .5 or .75 to 8%, but is preferably less than 4% The proportion of chromium mo may also vary widely, say from 6% to 15%, but is preferably less than 10%. The proportion of aluminum may vary from .5 to 7%, although the most desirable percentage is from 1.5 to 3.5%. The proportion of silicon may vary from .3 to 4%, although a range of 1% to 1.8% is preferred. The proportion of manganese may vary from .25 to 2%, although .35 to .65%- is preferred. These proportions of silicon and manganese do not or usual range of alloy steel making practice.

The most desirable percentage of carbon is from .3 to .6%, although this percentage may be reduced to .25% and, in special cases, raised to 1.25%. Ordinarily, however, the carbon content should not exceed 315%.

It must be borne in mind, however, that the proportions of certain oi. the ingredients should not be varied arbitrarily within the ranges specifled, but certain of them should have certain ratios, variable within limits, and dependent on the qualities, especially the critical temperature, desired.

I submit herewith, in the first three columns, three specific valve compositions, in the fourth column a desirable range of proportions, and in the last column what may be considered, except perhaps in very special cases, an extreme range ofproportrons:

.51 .48 .4 .am .00 mm in are 9.30 9.5 s tol2 a mic 3.33 1.18 1.2 1 to 3.6 .5 to 8 3.28 2.12 1.8 1.5 to 2.26 .5 to 5 .42 .61 .4 .35to .65 .2 to 2 .40 1.05 1.5 1 m 1.8 .3 to 4 Compositions not varying widely from the sec- .ond composition are, perhaps, preferable for most uses.

In these compositions, as previously stated, the aluminum has a distinct hardening effect through the nickel which is present and which is entirely diiferent from its action upon alloys free from nickel, and it raises the critical hardening range, which tends to keep the valve head from cracking due to change 01' size in passing through this range.

Furthermore, the material is exceptionally resistant to scaling at high temperature, and the scale which forms has a tendency to adhere to the metal and not drop oil. This is of great advantage in securing continuous good seating of a valve.

By heating to a very high heat and then quenching the end, the valve stem, moreover, is sufliciently hard to withstand the blows of the tappets.

Notwithstanding all-the above advantages, the composition does not contain expensive ingredients in high proportions, permitting the manufacture of valves at reasonable cost.

It is believed that the composition herein disclosed is novel, but it should be understood that aside from the novelty of the composition, specific novelty also resides in the discovery that said composition is especially adapted to the manufacture 01' valves, in that valves of the disclosed composition possess a combination of qualities and advantages that have never hitherto charac-e terized any alloy steel that is marketable at a reasonable price, and that the especial adaptability of the disclosed composition to the manufacture of valves, as distinguished from numerous other articles that are fabricated from alloy steels of various composition, is not obvious and cannot be determined without thorough tests under adverse conditions.

In determining the proportions of certain ingredients, the temperature conditions to which the valves are subjected should be borne in mind. Some valves, as, for example, those used in Diesel engines, are subjected to a much lower maximum temperature than the valves used in airplane engines. The required critical temperature of the steel may vary from 1400 to 1800 or possibly 1900 F. Starting with a chromium alloy steel having a critical temperature of about 1600 F., my experiments, for which a certain margin of error must be allowed, indicate that not only must suflicient nickel and aluminum be added to secure the known functions of nickel and aluminum respectively, but they must be added in proportions more or less nearly equal to maintain that critical temperature. The permissible proportion of each may vaiy widely pro- .vided substantial equality oi proportions is main- With a ratio of about 1 :1 (Ni to Al) critical temperature remains at 1600 F. With a ratio of 110.4 (Ni to Al) critical temperature becomes 1500" F.

With a ratio of 111.9 (Ni to Al) critical temperature becomes 1700 F. With a ratio of 1 :2.7 5 (Ni to Al critical tem With a ratio of LI. :3.90 (Ni to A critical temperature becomes 1900" F.

It should be understood that this table is based on my own experiments and that other experiments may yield a somewhat diilferent result; but the table is reliable as indicating, with an approximation to accuracy, the eilfects of varying the ratios of nickel to aluminum.

It should also be understood that, as before explained, the presence of chromium, which as before explained affects materially the critical temperature reducing efl'ectof nickel, afiects the required ratios between nickel and aluminum,

) )rature becomes 1800 F.

and that therefore the greater the percentage of chromium, the smaller the permissible percentage of nickel, in order to secure a given critical temperature for the alloy. The presence of chromium thus affects the required ratio between nickel and aluminum.

It should also be understood that the per centage of silicon aflects the critical temperature, that my composition requires no high silicon content, and that it is possible to produce alloy steel embodying my invention and containing a percentage of silicon that is within the lower part of the range of alloy steel making practice. Since silicon and manganese are present in nearly all carbon steels, my invention may be said to comprise, broadly, the addition, to carbon steel (of which the carbon content should generally be less than one per cent.) of chromium 6 to less than 15%, nickel .5 to 8% and aluminum .5 to 7%; the proportions of aluminum and nickel, and also the ratio of one to another, varying with the critical temperature desired, as above explained. While the percentage of carbon may, in exceptional cases, exceed one per cent, valves that will meet requirements to the fullest degree should comprise the constituents named in the following proportions: carbon not over about or under about 0.25% and preferably from 0.35 to .6%; nickel, between 1 and 4%, preferably not over 3.5%; chromium within, or at any rate not far outside, the range 8 to 11 or 12%; and aluminum 1 to 4% and preferably with the range 1.5% to 2.5%.

While the proportions of the different ingredients may vary within a fairly wide range, it

must be understood, as hereinbefore explained, that a low or high percentage of one ingredient may not be associatable with respectively high or low percentages of every other ingredient. This is particularly true of aluminum in its relation to nickel, and to nickel and chromium combined. Thus, the percentage of nickel should not be inexcess of 2.5 times thepercentage of aluminum: and in most instances the percentage of aluminum should not be substantially less, or should substantially exceed, the percentage of nickel, as in the specific illustrative compositions hereinbefore given. 80, also, the percentage of aluminum should be at least one-ninth, and usually should be at least one-sixth, the percentage of nickel and chromium combined.

There is no novelty in the present process so far as concerns the procedure of mixing the ingredients, melting, heat treating, etc., which may follow established practice of making steel alloys,

the noveltyresiding in the proportioning of the ingredients and in varying such absolute and relative proportions in accordance with the critical temperature desired.

I am aware of the fact that alloys are known containing chromium from 15 to 25%, nickel from'5 to 10%, aluminum from V to 2%, and high carbon .above 1%, the ratio of aluminum to nickel varying from 1 to from 5 to ,10. Such alloys are intended for heavy castings, such as parts of oil stills, and it is not practicable to forge them, nor are they intended to be forged. They are said to be of value where rigidity under a heavy load at high temperatures is a desideratum. They are, however, wholly valueless to secure the qualities desirable in valves and in other forged articles subject to similar requirements and conditions of use. I am also aware of the fact that alloys are known containing chromium 10 to 15%, nickel 4 to 10%. and titanium .2 to 4%, with ordinary proportions of silicon and manganese. The only aluminum that small proportion which is present in the term-- chrome if it is made by the thermite process. Such alloys are said to be malleable only if the carbon be reduced as low as .11 or .12% and easily machinable onlyif the carbon is reduced to about .08%. In my composition. the percentage of nickel rarely approximates as high as four per cent; the amount of aluminum is rarely less than 40% of the amount of nickel and when a medium 'or high critical temperature is desired the percentage of aluminum substantially exceeds the percentage of nickel; and although the percentage of carbon is never less than .2% and is.usually between .35 and .60% and may approximate. .1%, the alloy is both malleable and machinable.

I also disclaim as my invention any composition containing 5% or. more of nickel, unless the percentage of nickel is less than 2.5 times the percentage of aluminum. Exceptionally, an alloy containing as high as 5%, but not over 8%, nickel will have, in degree, qualities characteristic of my invention; but in no case will it poses such qualities if the proportion of nickel to aluminum exceeds that specified. A composition defined, broadly, as containing, as essential alloying innovelty on proportions of the constituent metals, and although these are .variable within fairly wide ranges, they cannot be varied to the extent that all the ingredients of the composition would be brought within the ranges above specified. The requirements of a perfect valve, namely, resistance to scaling at high temperature, resistance to upsetting and deformation, prevention of seizure in their bearings, and maintenance of structure and size and shape under high tempera- I tures with subsequent cooling, are all possessed by valves constructed in accordance with my composition, although the required combination of qualities is entirely absent if the desirable proportions of the ingredients are departed from to a degree that would produce an alloy whose ingredients are within the proportions of known alloys composed of the same metals. Thus, in the-known alloy to which reference is made, while great hot hardness is secured by the high nickel and high carbon content, the association of these ingredients with a high chromium content and an aluminum content that is low compared with the nickel content would reduce the critical temperature of the alloy below a practicable limit, making the steel austenitic at ordinary temperatures, and would fail to approximate the other desired valve characteristics even as closely as other valve compositions heretofore known.

What I claim and desire to protect by Letters Patent is:

1. A hard steel alloy containing carbon about .2 to less than 1%, nickel about .5 to 8%, chromiumv about 6 to less than 15%, and aluminum about .5 to 7%, the remainder being substantial-' ly iron, the percentage of nickel being less than 2.5 times the percentage of aluminum; said alloy having a critical temperature not less than about 1400 F. and having the characteristics of resistance to alterations in structure, size and shape with great temperature changes, retention of hardness at elevated temperatures, freedom from scaling, resistance to deformation, and which is readily malleable and machinable. 12

2. A hardened valve adapted for use in internal combustion engines and composed of a readily malleable and machinable steel alloy having a critical temperature not less than 1400" F. and containing carbon about .2 to less than 1%, nickel about .5 to 8%, chromium about 6 to less than 15%, and aluminum about .5 to 7%,- the remainder being substantially iron, the percentage of nickel being less than 2.5 times the percentage of aluminum; 'said valve having the characteristics of resistance to alteration in structure, size and shape with great temperature changes, retention of hardness and resistance to scaling at elevated temperatures, resistance to upsetting and to deformation under impact, and avoidance of seizure and galling of the valve stem in its guides.

3. A steel alloy comprising carbon'about .2 to 1.25%, nickel about .5 to less than 4%, chromium about 6 to less than 15%, and aluminum about .5 to 5%, the remainder being substantially iron.

4. A steel alloy comprising carbon about .2 to 1.25%, nickel about .5 to-less than 5%, chromium about 6 to less than 15%, and aluminum 145 about .5 to 7%, the remainder being substantially iron. v

5. A steel alloycomprising carbon about .2 to 1.25%, nickel about .75 to less than 4%, chromium about 6 to lessthan 10% and aluminum 150 about 1 to 7%, the remainder being substantially iron.

6. A steel alloy comprising carbon about .2 to 1.25%, nickel about .5 to 7%, chromium about 6 to less than and aluminum about .5 to 7%, the remainder being substantially iron; the percentage of nickel not substantially exceeding the percentage of aluminum.

7. A steel alloy comprising carbon about .2 to 1.25%, nickel about .75 to less than 4%. chromium about 6 to less than 15%, and aluminum about 1 to 7%, the remainder being substantially iron; the percentage of aluminum being substantially in excess of the percentage of nickel.

8. A steel alloy comprising carbon about'.2 to less than 1%, nickel about .5 to less than 5%, chromium about 6 to less than 15%, and aluminum over .3 and less than 7 the remainder being substantially iron; the percentage of aluminum being not less than one-ninth of the percentage of chromium and nickel combined.

9. A steel alloy comprising carbon about .2 to 1.25%, nickel about .5 to less than 5%, chromium about 6 to less than 15% and aluminum over .3 and less than 7%, the remainder being substantially iron; the percentage of aluminum being not less than one-sixth the percentage of chromium 'and nickel combined.

10. A steel alloy comprising carbon about .2 to less than 1%, nickel about .75 to less than 4%, chromium about 6 to less than 15%, aluminum over .3 and less than 7%, the remainder being substantially iron; the percentage of aluminum being not less than one-ninth of the percentage of chromium and nickel combined.

11. Asteel alloy comprising carbon about .2 to 1.25%, nickel about .75 to less than 4%, chromium about 6 to less than 15%, and aluminum over .3 and less than 7%, the remainder being substantially iron; the percentage of aluminum being not less than one-sixth the percentage of chromium and nickel combined.

12. A steel alloy containing carbon about .2 to .9%, nickel over .5 to less than 4%, chromium about 6 to less than 15%, and aluminum over 2 to less than 7%, the remainder being substantially iron.

13. A malleable steel resistant to hot oxidation containing efiective amounts of chromium, nickel, and aluminum as essential alloying ingredients, the sum of the chromium and nickel contents ranging up to 18%, the nickel content being less than 5%, the chromium content being over 6% and less than 15%, and the aluminum content being over .3% and not over about 5%; the remainder being substantially iron.

14. A malleable steel resistant to hot oxidation containing eflective amounts of chromium, nickel, and aluminum as essential alloying ingredients, the sum 01' the chromium and nickel contents ranging from 10 to 12.5%, the nic el content being less than 5% and the alumin content ranging from 1.5 to 2%; the remainder being substantially iron.

15. Amalleable steel resistant to hot oxidation containing effective amounts of chromium, nickel, and aluminum as essential alloying ingredients, the sum of the chromium and nickel contents ranging up to 18%, the chromium content being over 2%, the nickel content being less than 5%, and the aluminum content being between .3 and 3%; the remainder being substantially iron.

16. A malleable steel resistant to hot oxidation containing effective amounts of chromium, nickel, and aluminum as essential alloying ingredients, the sum of the chromium and nickel contents being less than 20%, the nickel content being less than 5%, the chromium content being over 2%, and the aluminum content being over .3% and not over about 5%; the remainder being substantially iron.

17. A hard steel alloy containing carbon .2 to 1.25%, nickel .5 to less than 5%, chromium 6 to less than 15%, and aluminum over .3 to less than 7%, the remainder being substantially iron, the percentage of nickel being less than 2.5 times the percentage of aluminum; said alloy having a critical temperature not less than about 1400 F. and having the characteristics of resistance to alterations in structure, size and shape with great temperature changes,- retention of hardness at elevated temperatures, freedom from scaling, resistance to deformation, and which is readily malleable and machinable.

18. A hardened valve adapted for use in internal combustion engines and composed of a readily malleable and machinable steel alloy having a critical temperature not less than 1400 F. and containing nickel .5 to less than 5%. chromium 6, to less than 15%, and aluminum over .3 to less than 7%, the remainder being substantially iron, the percentage of nickel being less than 2.5 times the percentage of aluminum; said valve having the characteristics of resistance to alteration in structure, size and shape with great temperature changes, retention of hardness and resistance to scaling at elevated temperatures, resistance to upsetting and to detormation under impact, and avoidance of seizure and galling of the valve stem in its guides.

JOHN L. COX. 

